Dicing of semiconductors

ABSTRACT

In the manufacture of semiconductors by forming a large number of devices on one wafer, protecting the individual devices by wax masks and then subjecting the wafer to an etching acid to separate the devices, apparatus is used for separating the wafers comprising a tray on which the wafer is placed. Means is provided for circulating an etching acid in a path including the tray, and in this path there is means for controlling the temperature of the acid.

United States Patent m1 3,632,462

[72] Inventor Colin Arthur Harrington [50] Field of Search 156/345, 17

Sutton Coldfield, England [21] Appl. No. 797,610 Relerences Cited [22] Filed Feb. 7, 1969 UNITED STATES PATENTS Patented Jan. 4, 1972 std Limited 3,095,463 6/ 1963 Chang et al [56/345 UX [73] Amgnee g es) Primary Examiner-Jacob H. Steinberg 32 Priority Feb. 9, 1968 5mm [3 3] Great Britain ABSTRACT: In the manufacture of semiconductors by forming a large number of devices on one wafer, protecting the in- [54] meme 0F SEMCONDUCTORS dividual devices by wax masks and then subjecting the wafe;

4 Claims 1 Dnwing a. to an etchrng acid to separate the devices, apparatus IS use for separating the wafers compnsmg a tray on which the wafer [52] US. Cl. 156/345, is placed, Means is provided for circulating an etching acid in 156/17 a path including the tray, and in this path there is means for [5] 1 Int. Cl. controlling the temperature of the acid HE T /4 PUMP EXCHANGE? rmmeum 41972 31632462 L? 15 i5? EXCHANGEE I/ H i 15 PUMP /7 {9 INVE TO? I xi" AWO ENEYS meme F SEMICONDUCTORS In the manufacture of semiconductors it is common to form a large number of devices on one wafer, then to protect the individual devices by wax masks and to subject the wafer to an etching acid to separate and dice the devices. This invention relates to apparatus for performing the etching operation.

Apparatus according to the invention comprises a tray on which the wafer is placed, means for circulating an etching acid in a path including said tray, and means in said path for controlling the temperature of the acid.

The usual arrangement is merely to pour acid into the tray without any circulation or temperature control. For this reason the life of a given batch of acid is limited, because if the acid temperature is too low the etching time is increased, but if the acid temperature becomes too high, the wax masks tend to become lifted from the wafer. Using the conventional technique, a typical arrangement using three liters of acid will etch 20 wafers. An arrangement in accordance with one example of the invention using 12 liters of acid which was circulated was found to etch successfully 160 wafers of the same size, an overall improvement of 100 percent.

An example of the invention is illustrated diagrammatically in the accompanying drawing.

Referring to the drawing, there is provided a tray 11 in which wafers to be etched are placed, the tray having an inlet for a suitable etching acid, and an outlet, so that acid flows through the tray continuously. A suitable acid is of known fon'n including nitric acid, hydrofluoric acid and acetic acid. From the outlet, acid flows to a reservoir 12, from which a pump 13 supplies the acid to a water-cooled heat exchanger 14, which in turn supplies the acid to the inlet of the tray. The outlet of the pump may be connected to the tray through some form of valve 15 to control the amount of acid supplied to the tray.

Between the outlet of the tray and the reservoir 12 is a temperature probe 16 for sensing the temperature of the acid leaving the tray, the probe being connected to a solenoid which operates a valve controlling the amount of water flowing to the heat exchanger. Water is circulated from a reservoir 17 to the heat exchanger 14 by a pump 18 at a rate determined by a valve 19 which in turn is controlled by a solenoid 21 connected to an controlled by the probe 16. The arrangement is such that the acid is kept at a constant temperature which is chosen to be sufficiently low to avoid removal of the wax masks on the wafer, but sufficiently high to ensure that etching takes place at an acceptable rate. A suitable temperature using a typical wax having a melting point of C. is in the range 10 to 14 C., preferably.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. ln an apparatus for performing a separation etching operation on a wax-masked semiconductor wafer, to dice said wafer comprising a tray on which the wafer is placed and means for circulating an etching acid in a path including said tray, the improvement comprising cooling means in said path for controlling the temperature of the acid.

2. Apparatus as claimed in claim 1 in which a pump supplies acid to the tray through a heat exchanger, the temperature of the etching acid being sensed by a temperature probe which controls the rate of supply of coolant to the heat exchanger.

3. Apparatus as claimed in claim 2 including a valve for controlling the rate of flow of the etching acid.

4. In a method of dicing semiconductors, said method comprising the steps of forming a number of devices on one wafer; applying wax masks to the individual devices to protect the individual devices; placing the devices on a tray and circulating etching acid therethrough; the improvement comprising cooling the circulating etching acid. 

1. In an apparatus for performing a separation etching operation on a wax-masked semiconductor wafer, to dice said wafer comprising a tray on which the wafer is placed and means for circulating an etching acid in a path including said tRay, the improvement comprising cooling means in said path for controlling the temperature of the acid.
 2. Apparatus as claimed in claim 1 in which a pump supplies acid to the tray through a heat exchanger, the temperature of the etching acid being sensed by a temperature probe which controls the rate of supply of coolant to the heat exchanger.
 3. Apparatus as claimed in claim 2 including a valve for controlling the rate of flow of the etching acid.
 4. In a method of dicing semiconductors, said method comprising the steps of forming a number of devices on one wafer; applying wax masks to the individual devices to protect the individual devices; placing the devices on a tray and circulating etching acid therethrough; the improvement comprising cooling the circulating etching acid. 